1. Field of the Invention
The present invention relates to mills for grinding or milling grains such as wheat, rice, corn, oats, rye, barley and coffee. More particularly, the present invention is a portable flour mill for use by a small bakery.
2. Discussion of Background
There exists in the art a variety of different rotary grinding mills for grinding wheat, corn, rye, oats, barley, rice, coffee and other grains. Mills have been known for centuries. Currently, small portable mills are used by smaller bakeries to mill grains for specialty breads. Mill technology is very traditional. Typically, such machines comprise a cast iron housing with a pair of circular, pink granite grinding stones, spaced a preselected, small distance apart. One of the stones, commonly referred to as the "running stone," is turned by a shaft, while the other stone, the "bed" stone, remains stationary. Grain is fed into the mill from a hopper to a rotating auger, and then into the space defined by the separation between the opposing faces of the stones. After the grain is milled to flour, the flour is removed from the interior of the mill for collection and further processing.
One problem repeatedly encountered in the art is the durability of the moving components of the mill. In particular, the shaft can be seized by the cast iron ball bearing assemblies through which the shaft is journaled when frictional heat welds the bearings to the shaft. Also, vibration from the motor that turns the shaft along with misalignment of the running stone causes the turning shaft to deviate from its normal, horizontal position, resulting in interference, frictional heat buildup, and excessive wear. In addition, heat from friction can damage the grain, as will be explained below.
If the machine is run continuously, heat builds in the housing and heats the grain. When the grain becomes overheated, it begins to break down chemically. For example, when wheat embryo, or the wheat kernel, experiences a temperature of approximately 130.degree. F. or greater, it loses its protein content. Furthermore, products made from overheated wheat flour are less flavorful. To limit heat buildup as well as prevent damage to moving parts, the running stone is rotated at a slower speed and for shorter periods of time to allow dissipation of the heat. However, neither of these solutions is acceptable, since both adversely affect the productivity of the grinding operation.
Another problem is the existence of metal particles that chip off the hopper and fall into the wheat. Most mills sift the wheat, as has been done for decades, to remove stones and other foreign particles. However, metal particles are not removed. These contact the stone faces and produce surface irregularities that affect the surface of the grinding stones and require them to be smoothed and flattened, or "dressed," more frequently. In addition, failure to remove these metal particles prior to milling affects flour quality.
Size inconsistencies in the milled product are yet another problem faced by the industry. Normally, the distance between the grinding stones, and hence the resulting fineness of the milled product, is adjusted by using a threaded screw, usually having eight threads per inch, which is positioned to abut the end of the turning shaft. Turning the screw moves the shaft, and thus the relative positions of the running and bed stones. Rotation of the shaft exerts a force in the direction of the screw that, over time, wears on the screw's threads. Eventually, the adjustment screw cannot be relied on to accurately maintain the correct separation of the stones, and as a result, the output from the mill contains particles of non-uniform size.
Because of the traditional approach to mill manufacture, the problems of heat buildup, frequent breakdowns, low output, and uneven quality of the output have not been addressed. There exists a need for a durable mill that produces a high quality product with high productivity.